Research on the causes and policy implications of fertility decline and differentials in the United States has been hampered a lack of comparable, long-term fertility estimates and a focus on short-term factors. This project will: (1) produce a consistently constructed and comparable set of fertility trends and differentials between 1790 and 2000;and (2) construct empirical models to understand the processes by which fertility declined. The analysis relies on data from two complementary sources: The Integrated Public Use Microdata Series (IPUMS), a series of large, high-precision census microdata samples for fifteen census years between 1850 and 2000, and the National Historical Geographic Information System (NHGIS) project, a compatible dataset of aggregate data collected with the 1790-2000 censuses. The proposed development plan is designed to accomplish four objectives: 1) to acquire new methodological skills to allow me to accurately describe and explain long-term fertility decline in the United States;2) to acquire a better theoretical grounding from which to integrate social and economic explanations of why American fertility declined;3) to present my work at scholarly conferences and publish in leading journals;and 4) to prepare a grant proposal to support an independent research program. My plan includes three separate training components: mentorship by leading demographers and economists, coursework in demography at the University of Pennsylvania, and participation in the population research community via workshops and seminars at the Pennsylvania Population Studies Center and annual meetings of the Population Association of America.